Method and device for charging battery

ABSTRACT

A method for charging a battery includes: determining a first charging section, in which a current charging rate of the battery is located, from among a plurality of charging sections predetermined based on a functional relation between a state of charge of the battery and an open circuit voltage of an anode of the battery; and charging the battery for the first charging section with a first charging rate corresponding to the first charging section.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/879,883, filed on Jan. 25, 2018, which claims priority to KoreanPatent Application No. 10-2017-0016870, filed on Feb. 7, 2017, and allthe benefits accruing therefrom under 35 U.S.C. § 119, the content ofwhich in its entirety is herein incorporated by reference.

BACKGROUND 1. Field

The disclosure relates to a method and device for charging a battery bychanging a charging rate with multiple stages.

2. Description of the Related Art

Various types of charging algorithms for improving a charging speed of abattery have been suggested. In general, a constant current-constantvoltage (“CC-CV”) charging scheme is varied, or a method that is similarto the CC-CV charging scheme is combined, and there are algorithms suchas a pulse charging, a boost charging, and a multi-stage constantcurrent charging.

The pulse charging scheme represents a method for applying a highcurrent to the battery for a predetermined time, and providing a pauseperiod (or a discharge time). According to the pulse charging scheme, aconcentration of lithium ions on a surface of an active material isincreased through a high-level current applied in an initial chargingstage thereby acquiring a maximum spread speed, and a concentrationdistribution of lithium ions are relaxed through a discharging (or arelaxation) thereby controlling an additional side reaction. In a pulsecharging scheme, the pulse charging scheme includes a section duringwhich no actual charging is performed (a pause or discharge section)represented by a duty cycle, so there is a limit in improvements ofcharging speed.

The boost charging scheme applies a high current in an earlier stage togenerate a high voltage, and charges with a constant voltage for apredetermined time, and then performs a CC-CV charging. According to theboost charging scheme, the completely discharged battery has highhigh-rate adaptation performance in the earlier stage of charging, so aconstant voltage charging is performed up to the 30% of charging rate,and a voltage that is higher than a voltage at a constant voltagesection in a latter portion to perform a charging with a high current.The boost charging scheme uses an initial battery state, in which thebattery is very close to a complete discharging in consideration of thehigh current applying stage, in the earlier charging stage.

In such a conventional charging schemes, an algorithm that uses aninitially input charging condition to check the dischargecharacteristics and adjust the initial input charging condition based ontrial and error, or states (temperature, temperature change, voltage, orvoltage change) of the battery according to the applied current aremeasured and the value of the current is desired to be controlled, sorisks of time and experiments for confirmation of the algorithmincrease, and an additional system for an adaptive-scheme controlling isused, thereby increasing complexity of application.

SUMMARY

A multi-stage constant current scheme divides the time axis into aplurality of sections, and applies currents from a higher current to alower current as the respective sections are in progress. Division ofrespective sections follows a predetermined threshold voltage, and whenthe charging voltage reaches the threshold voltage, the size of thecurrent is changed (i.e., a lower current is applied). The sizes ofcurrents for respective sections are determined by various optimizationtools, and in general, an optimized pattern is determined by repeatingthe process for checking discharge characteristics after a firstapplication of a profile. By dividing the respective stages by a voltageand changes of current intensity, various types of algorithms may bededuced. The key aspect of the multi-stage constant current scheme is toset a section for maintaining capacity of the battery while maximizingthe charging speed, and determine charging rate intensities forrespective sections.

Exemplary embodiments of the invention are directed to a method forcharging a battery using a multi-stage constant current scheme.

Exemplary embodiments of the invention are directed to a device forcharging a battery by use of a multi-stage constant current scheme.

An exemplary embodiment of the invention provides a method for charginga battery including: determining a first charging section, in which acurrent charging rate of the battery is located, from among a pluralityof charging sections predetermined based on a functional relationbetween a state of charge (“SOC”) of the battery and an open circuitvoltage (“OCV”) of an anode of the battery; and charging the battery forthe first charging section with a first charging rate corresponding tothe first charging section.

In an exemplary embodiment, the battery charging method may furtherinclude charging the battery for a second charging section, which isnext to the first charging section from among the plurality of chargingsections, with a second charging rate corresponding to the secondcharging section when the first charging section ends.

In an exemplary embodiment, the battery charging method may furtherinclude monitoring whether a charging voltage of the battery has reacheda predetermined voltage value when the first charging section is thelast charging section from among the plurality of charging sections or asecond charging section, which is next to the first charging sectionfrom among the plurality of charging sections, is the last chargingsection; and applying a maximum charging voltage to the battery when thecharging voltage reaches the predetermined voltage value.

In an exemplary embodiment, the plurality of charging sections may bedetermined based on a window with a predetermined height applied withreference to a minimum or a maximum of a differential graph of thefunctional relation included in the charging sections, and thepredetermined height may be predetermined according to complexity of acharging processor.

In an exemplary embodiment, the predetermined height may bepredetermined as a value equal to or less than 0.6.

In an exemplary embodiment, as the predetermined height increases, awidth of the window may increase to increase respective lengths of thecharging sections, and as the predetermined height decreases, the widthof the window may reduce to reduce the respective lengths of thecharging sections.

In an exemplary embodiment, as the predetermined height increases, awidth of the window may increase to reduce a number of the chargingsections, and as the predetermined height decreases, the width of thewindow may reduce to increase the number of the charging sections.

In an exemplary embodiment, the first charging rate may be maintained ata constant value for the first charging section, and a differencebetween a potential of an anode of the battery and a potential of anelectrolyte solution of the battery may be determined to be less than apredetermined value at an ending point of the first charging section.

In an exemplary embodiment, the predetermined value may be 2×10⁻⁶ volt(V).

In an exemplary embodiment, the first charging rate may be maintained ata constant value for the first charging section, and a differencebetween a potential of an anode of the battery and a potential of anelectrolyte solution of the battery may be determined to be greater thanzero (0) for the first charging section.

In an exemplary embodiment, a value of the first charging rate may begreater than a value of the second charging rate.

Another other embodiment of the invention provides a device for charginga battery including: a processor, a memory connected to the processor,and a charging interface connected to the battery, where the processorperforms a program stored in the memory to perform: determining a firstcharging section, in which a current charging rate of the battery islocated, from among a plurality of charging sections predetermined basedon a functional relation between an SOC of the battery and an OCV of ananode of the battery; and charging the battery for the first chargingsection with a first charging rate corresponding to the first chargingsection.

In an exemplary embodiment, the processor may perform the program storedin the memory to further perform charging the battery for a secondcharging section, which is next to the first charging section from amongthe plurality of charging sections, with a second charging ratecorresponding to a second charging section when the first chargingsection is finished.

In an exemplary embodiment, the processor may perform the program storedin the memory to further perform: monitoring whether a charging voltageof the battery has reached a predetermined voltage value when the firstcharging section is the last charging section from among the pluralityof charging sections or a second charging section, which is next to thefirst charging section from among the plurality of charging sections, isthe last charging section; and applying a maximum charging voltage tothe battery when the charging voltage reaches the predetermined voltagevalue.

In an exemplary embodiment, the charging sections may be determinedbased on a window with a predetermined height applied with reference toa minimum or a maximum of a differential graph of the functionalrelation included in the charging sections, and the predetermined heightmay be predetermined according to complexity of a charging processor.

In an exemplary embodiment, the predetermined height may bepredetermined as a value equal to or less than 0.6.

In an exemplary embodiment, as the predetermined height increases, awidth of the window may increase to increase respective lengths of thecharging sections, and as the predetermined height decreases, the widthof the window may reduce to reduce the respective lengths of thecharging sections.

In an exemplary embodiment, as the predetermined height increases, awidth of the window may increase to reduce a number of the chargingsections, and as the predetermined height decreases, the width of thewindow may reduce to increase the number of the charging sections.

In an exemplary embodiment, the first charging rate may be maintained ata constant value for the first charging section, and a differencebetween a potential of an anode of the battery and a potential of anelectrolyte solution of the battery may be determined to be less than apredetermined value at an ending point of the first charging section.

In an exemplary embodiment, the predetermined value may be about 2×10⁻⁶V.

In an exemplary embodiment, the first charging rate may be maintained ata constant value for the first charging section, and a differencebetween a potential of an anode of the battery and a potential of anelectrolyte solution of the battery may be determined to be greater thanzero (0) for the first charging section.

In an exemplary embodiment, a value of the first charging rate may begreater than a value of the second charging rate.

According to the exemplary embodiments of the invention, the lithiumplating phenomenon of the battery may be effectively prevented fromoccurring by charging the battery based on the charging section and thecharging rate corresponding to the charging section, which aredetermined based on the change of the OCV of the anode material of thebattery.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other features of the invention will become apparent andmore readily appreciated from the following detailed description ofembodiments thereof, taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 shows a flowchart of a battery charging method according to anexemplary embodiment;

FIG. 2 shows a graph of a relationship between a state of charge (“SOC”)of a battery and an open circuit voltage (“OCV”) of an anode accordingto an exemplary embodiment;

FIG. 3 shows a charging section determined by a relationship between anSOC of a battery and an OCV of an anode according to an exemplaryembodiment;

FIG. 4 shows a flowchart of a method for determining charging rates forrespective charging sections according to an exemplary embodiment;

FIG. 5 shows a graph for charging rates and potential difference(“dphisl”) for respective charging sections according to an exemplaryembodiment;

FIG. 6 shows a graph of charging rates applicable at an actual chargingtime, dphisl, and changes of charging voltages according to an exemplaryembodiment;

FIGS. 7A and 7B show a graph of a charging section and a charging rateapplied to an LCO/Ni—Sn battery cell according to an exemplaryembodiment;

FIG. 8 shows a comparison graph of changes of charging voltages of anLCO/Ni—Sn battery cell according to an exemplary embodiment;

FIG. 9 shows a graph of changes of a thickness of an SEI thin film of anLCO/Ni—Sn battery cell according to an exemplary embodiment;

FIG. 10 shows a graph of a charging section applied to an LCO/graphitebattery cell according to an exemplary embodiment;

FIG. 11 shows a graph of a comparison result of capacity retention of anLCO/graphite battery cell according to an exemplary embodiment; FIG. 12Ato FIG. 12C show graphs of changes of dphisl with respect to chargingsection, charging rate, and time of an LCO/graphite battery cellaccording to an exemplary embodiment;

FIG. 13 shows a graph of comparison of changes of a charging voltage ofan LCO/graphite battery cell according to an exemplary embodiment;

FIG. 14 shows a graph of changes of a thickness of an SEI thin film ofan LCO/graphite battery cell according to an exemplary embodiment; and

FIG. 15 shows a block diagram of a battery charging device according toan exemplary embodiment.

DETAILED DESCRIPTION

The invention will be described more fully hereinafter with reference tothe accompanying drawings, in which exemplary embodiments are shown.This invention may, however, be embodied in many different forms, andshould not be construed as limited to the embodiments set forth herein.Rather, these embodiments are provided so that this disclosure will bethorough and complete, and will fully convey the scope of the inventionto those skilled in the art. Like reference numerals refer to likeelements throughout.

It will be understood that when an element is referred to as being “on”another element, it can be directly on the other element or interveningelements may be therebetween. In contrast, when an element is referredto as being “directly on” another element, there are no interveningelements present.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used herein, thesingular forms “a,” “an,” and “the” are intended to include the pluralforms, including “at least one,” unless the content clearly indicatesotherwise. “Or” means “and/or.” As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items. It will be further understood that the terms “comprises”and/or “comprising,” or “includes” and/or “including” when used in thisspecification, specify the presence of stated features, regions,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,regions, integers, steps, operations, elements, components, and/orgroups thereof.

Furthermore, relative terms, such as “lower” or “bottom” and “upper” or“top,” may be used herein to describe one element's relationship toanother element as illustrated in the Figures. It will be understoodthat relative terms are intended to encompass different orientations ofthe device in addition to the orientation depicted in the Figures. Forexample, if the device in one of the figures is turned over, elementsdescribed as being on the “lower” side of other elements would then beoriented on “upper” sides of the other elements. The exemplary term“lower,” can therefore, encompasses both an orientation of “lower” and“upper,” depending on the particular orientation of the figure.Similarly, if the device in one of the figures is turned over, elementsdescribed as “below” or “beneath” other elements would then be oriented“above” the other elements. The exemplary terms “below” or “beneath”can, therefore, encompass both an orientation of above and below.

“About” or “approximately” as used herein is inclusive of the statedvalue and means within an acceptable range of deviation for theparticular value as determined by one of ordinary skill in the art,considering the measurement in question and the error associated withmeasurement of the particular quantity (i.e., the limitations of themeasurement system).

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art and thedisclosure, and will not be interpreted in an idealized or overly formalsense unless expressly so defined herein.

Hereinafter, exemplary embodiments of the invention will be described indetail with reference to the accompanying drawings.

FIG. 1 shows a flowchart of a battery charging method according to anexemplary embodiment.

In an exemplary embodiment, the battery is charged based on themulti-stage constant current charging scheme. Referring to FIG. 1, in anexemplary embodiment, a battery charging device checks a charged amount(a state of charge or a charging voltage) of the battery, and selects acharging section corresponding to a residual charged amount (S110).

According to an exemplary embodiment, a plurality of charging sectionsfor charging a battery are determined based upon a relationship betweena state of charge (“SOC”) and an open circuit voltage (“OCV”) of ananode material of the battery. The charging section according to anexemplary embodiment will now be described in detail with reference toFIG. 2 and FIG. 3.

FIG. 2 shows a graph of a relationship between an SOC of a battery andan OCV of an anode according to an exemplary embodiment, and FIG. 3shows a functional relation between an SOC of a battery and an OCV of ananode, and a charging section determined by the functional relation.

In FIG. 2, the x-axis indicates an SOC of the battery, and the y-axisrepresents an OCV of an anode of the battery. The SOC of the battery isdetermined by a ratio of Li in the anode. Referring to FIG. 2, the OCVof the anode decreases as the SOC increases. In such an embodiment, whenthe charging is performed, a potential (phis) of an anode activematerial (a solid matter) decreases, and on the contrary, a potential(phil) of an electrolyte (a liquid) increases because of supplying oflithium positive ions. In such an embodiment, when the potential of theanode active material becomes equal to the potential of the electrolyte(phis=phil), lithium positive ions may be deposited. Therefore, alithium-plating (Li-plating) phenomenon may be effectively prevented byanalyzing a change of reduction of the OCV caused by a Li concentrationin the anode active material. The lithium plating phenomenon representsa phenomenon that lithium positive ions (Li+) supplied to the anode arenot quickly absorbed at the anode, but are accumulated and therebydeposited as a lithium metal, which is one of the most undesired aspectthat have to be considered when the battery is charged by applying ahigh charging rate (i.e., a high current rate (high charging rate)).When the lithium plating phenomenon occurs, non-uniform lithiumdendrites (Li-dendrite) may be formed, the battery may become shorted.Accordingly, the life-span of the battery may be reduced, and thebattery may be exploded. The lithium plating phenomenon occurs when thebattery is charged and a difference between the potential of the anodeactive material and the potential of the electrolyte is close to zero(0). Therefore, the lithium plating may be estimated by the change ofpotential of the anode according to the concentration of lithium in theanode active material.

According to an exemplary embodiment, a plurality of charging sectionsfor charging the battery may be determined or distinguished depending ona point at which a pattern of an OCV reduction (e.g., a slope of anSOC-OCV graph or a dOCV/dSOC graph) of the anode changes. In oneexemplary embodiment, for example, the charging section may bedetermined or distinguished with reference to the point where a slope ofthe OCV of the anode is analyzed with respect to the SOC (or time), anda difference of slopes becomes a predetermined value.

According to an exemplary embodiment, a peak point is determined basedon a differential graph (shown by a single dash-dot line) havingdifferentiated a functional relation of the OCV with respect to the SOC.When there is a minimum (a point at which the differential value changesfrom a negative value to a positive value) in the differential graph,the charging section is determined based on the minimum as a reference.Referring to FIG. 3, a point P₁ and a point P₂ on the differential graphcorrespond to the minimums. A window (a window in the (+) direction)with a height of S₀ is applied with reference to the respectiveminimums.

According to an exemplary embodiment, the window has a predeterminedheight So, and a width of the window is determined by a point where oneof an upper side and a lower side of the window meets the differentialgraph. The height So of the window is a predetermined value, e.g., avalue that is not greater than 0.6 according to a complexity of acharging process. In one exemplary embodiment, for example, when theheight S₀ is determined to be high, a width of the window increases toincrease a length of the charging section and reduce a number ofcharging sections included in the charging process. When the height S₀is determined to be low, the width of the window reduces to reduce thelength of the charging section and increase the number of chargingsections included in the charging process. Therefore, in a case wherethe charging process is desired to be simply controlled, the height S₀of the window is predetermined as a relatively greater value. In anothercase, where the charging process is desired to be precisely controlled,the height S₀ of the window is predetermined as a relatively less value.

Referring to FIG. 3, when the window with the height S₀ is applied tothe point P₁, a right border of the second charging section isdetermined, and when the window with the height So is applied to thepoint P₂, respective borders of the fifth charging section aredetermined. A left border of the point Pi may be determined by a maximum(a point at which the differential value changes from a positive valueto a negative value) since the maximum exists in the window applied tothe point P₁.

The window with the height S₀ is applied with reference to the maximum.Referring to FIG. 3, points P₃ and P₄ on the differential graphcorrespond to the maximum. The window (a window in a (−) direction) withthe height S₀ is applied with respect to a y-axis value of the maximum.Accordingly, a left border of the second charging section and a leftborder of the fourth charging section are determined. In FIG. 3, theright border of the first charging section is equal to the left borderof the predetermined second charging section, and the respective bordersof the third charging section are equal to the right border of thepredetermined second charging section and the left border of the fourthcharging section. That is, according to an exemplary embodiment, aborder of the charging section (the third charging section) thatmonotonically increases or monotonically decreases may be determined bya border of another charging section. In such an embodiment, in thesection (the sixth charging section) with a small variation of the OCV,the charging sections may not be divided although there exists a minimumor a maximum. In such an embodiment, the last charging section (e.g.,the sixth charging section) of the charging sections is a constantvoltage section, and the last charging section may be determinedaccording to another reference.

In such an embodiment, when the minimum and the maximum are within apredetermined range (i.e., when gaps of the minimum and the maximum issmaller than a predetermined value), it may be omitted to determine theborder by the maximum. In one exemplary embodiment, for example, in FIG.3, when the minimum P₁ and the maximum P₄ are included in apredetermined range, respective borders of the second charging sectionmay be determined by the window (a window in the (+) direction) with theheight S₀ with respect to the minimum P₁, or the right border of thesecond charging section may be determined by the window (a window in the(+) direction) with the y-axis value that is greater than the minimum P₁by S₀, and the left border of the second charging section may bedetermined by the window (a window in the (−) direction) with the y-axisvalue that is less than the minimum P₁ by S₀.

According to an exemplary embodiment, when the height So indicating thedifference between the slope corresponding to the border and the slopeof one of the minimum and the maximum is set to be a relatively bigvalue (e.g., 0.3), a section length of respective charging sectionsbecomes longer and the number of charging sections reduces so thecharging process may be simplified. Alternatively, when the height S₀ isset to be a relatively small value (e.g., 0.05), the section length ofrespective charging sections becomes shorter and the number of chargingsection increases so the battery may be further precisely charged. Inone exemplary embodiment, S₀ indicating the height of the window fordetermining a charging section may be determined to be less than apredetermined value (e.g., 0.5).

Referring to FIG. 3, the slope of the SOC-OCV graph in each section ismaintained to be relatively constant (a changing rate of the slope inthe section ≈0) or at a substantially constant value, but average slopesof respective sections have different values. That is, the changing rateof the slope of the border of each section has a relatively big valuethan the changing rate of the slope in each section (the changing rateof the slope of the border of the section >>0). In the section in whichthe changing rate of the slope is maintained at a relatively smallvalue, the battery charging device may relatively easily process thelithium-plating phenomenon. Therefore, a plurality of charging sectionsfor charging the battery may be determined by the slope of the SOC-OCVgraph or the changing rate of the slope, and the borders of respectivecharging sections when the battery is charged may be distinguishedaccording to the charging time or the charging voltage.

Referring back to FIG. 1, the battery charging device charges thebattery for the selected charging section with the charging rate (afirst charging rate) corresponding to the selected charging section (thefirst charging section) (S120). In an exemplary embodiment, the firstcharging section may be an m-th (m<n) charging section from among ncharging sections. Here, the charging rate (also known in the art asC-rate) represents a value for indicating the ratio of the chargingcurrent with respect to the capacity of the battery. Accordingly, whenthe size (or value) of the charging current corresponds to the capacityof the battery, for example, the charging rate is 1C.

The size of the charging rate corresponding to the respective chargingsections is determined to be the maximum size for preventing the lithiumplating phenomenon. According to an exemplary embodiment, the sizes ofthe charging rates corresponding to the respective charging sections aredetermined by a potential difference (dphisl) between the solid matterand the liquid of the anode and a surface of a separation layer. Thepotential difference (dphisl) between the solid matter and the liquidsatisfies the following Equation 1.

(Equation 1)

dphisl=phis−phil

In Equation 1, phis denotes a solid potential, that is, an anodepotential, and phil denotes a liquid potential, that is, an electrolytepotential. The dphisl is desired to be maintained to be always greaterthan 0, and it is determined in consideration of a design/manufacturingcondition and stability of the battery cell. The dphisl of the batteryis provided to be close to zero (0) at an end point of each chargingsection. When the dphisl of the battery reaches a predetermined dphislvalue U₀ (e.g., 2×10⁻⁶), the battery charging stage is changed to a nextcharging section, and the charging rate with a different size is appliedto the battery in the next charging section. In such an embodiment, whenthe first charging section ends, the battery charging device charges thebattery with a second charging rate corresponding to a second chargingsection during a time duration of the second charging section that isthe next charging section of the first charging section. In such anembodiment, the charging rate of the next charging section is less thanthe charging rate of a previous charging section.

FIG. 4 shows a flowchart of a method for determining charging rates forrespective charging sections according to an exemplary embodiment.

Referring to FIG. 4, in an exemplary embodiment, the size of the initialcharging rate of a specific charging section is randomly selected beforea battery charging simulation is performed (S410). In such anembodiment, the size of the initial charging rate may be selected to begreater than 10. A battery charging simulation for a specific chargingsection is performed based on the initial charging rate (S420), and thedphisl on a border of the specific charging section is checked (S430).

When the dphisl of the border of the specific charging section isgreater than U₀, the size of the charging rate is increased to performthe battery charging simulation (S440) because the fact that the dphislis greater than U₀ means that the battery may endure the high currentrate charging. In such an embodiment, when the dphisl of the border ofthe specific charging section is less than U₀, the size of the chargingrate is reduced to perform the battery charging simulation (S450)because the fact that the dphisl is less than the U₀ means that anexcessive charging rate is applied to the battery, which may generate alithium plating. When the dphisl becomes equal to U₀, the size of thecharging rate at that time is determined to be the charging rate in thecorresponding charging section, and the stages starting from S410 beginsto determine the charging rate of the next charging section (S460).

FIG. 5 shows a graph for charging rates and dphisl for respectivecharging sections according to an exemplary embodiment.

Referring to FIG. 5, the x-axis represents the time, and the y-axisindicates the charging rate and the size of dphisl. Here, the chargingrate represents a relative current size with reference to the currentsize of discharging the battery for one hour. FIG. 5 shows that thedphisl is quickly reduced in the initial charging section to which ahigh-level charging rate is applied.

In such an embodiment, the first charging section may be the last n-thcharging section (m=n) from among n-numbered charging sections, or thesecond charging section may be the last charging section. When thecurrent charging section is the last charging section (S130), thebattery charging device charges the battery with the n-th charging ratecorresponding to the n-th charging section, and monitors the chargingvoltage of the battery to check if the charging voltage of the batteryhas reached a predetermined voltage value for the charging section(S140). In such an embodiment, the predetermined voltage value may beexpressed with a predetermined ratio (e.g., 99%) for a maximum chargingvoltage (V_(max)), and the predetermined ratio and the maximum chargingvoltage are determined by considering the cathode, the anode, and thephysical property of the electrolyte. In an exemplary embodiment, thebattery charging device may adaptively lower the predetermined ratioaccording to a worn-out degree of the battery or an elapsing time.

When the charging voltage of the battery has reached a predeterminedvoltage value, the battery charging device may stop applying of aconstant current and may apply the maximum charging voltage to thebattery (a constant voltage stage) (S150). In such an embodiment, it maybe determined whether to enter the constant voltage stage based ondesign variables of the battery cell and an available maximum range ofthe SOC. When the constant voltage is applied, the battery chargingdevice may terminate the constant voltage stage with reference to thelowest current value (generally 0.05C). When the charging of the batteryis finished as the constant voltage stage is terminated, the currentapplied to the battery is intercepted by a current control device. Whenthe constant voltage stage is omitted, the battery charging device maycontrol the size of the n-th charging rate so that the charging voltagemay not exceed the maximum charging voltage. That is, the size of thecharging rate may be controlled so that the charging voltage of thebattery may reach the maximum charging voltage when the desired chargingSOC is achieved.

FIG. 6 shows a graph of charging rates applicable at an actual chargingtime, dphisl, and changes of charging voltages according to an exemplaryembodiment.

Referring to FIG. 6, when the battery is charged with a constantcharging rate in each charging section, the dphisl is maintained to begreater than a predetermined value dphisl0 in the entire section, andthe charging voltage rapidly increases. The charging section and thecharging rate determined according to the above-described methodrepresent values determined according to the characteristic of the anodematerial, and when the optimized algorithm for the charging section andthe charging rate determined by a numerical modeling is applied to theactual battery, a length of the charging section or the size of thecharging rate may be controlled in detail to reduce an error caused by aprocessing deviation of the battery.

FIGS. 7A and 7B show graphs of a charging section and a charging rateapplied to an LCO/Ni—Sn battery cell according to an exemplaryembodiment, FIG. 8 shows a comparison graph of changes of chargingvoltages of an LCO/Ni—Sn battery cell according to an exemplaryembodiment, and FIG. 9 shows a graph of changes of a thickness of an SEIthin film of an LCO/Ni—Sn battery cell according to an exemplaryembodiment.

In FIGS. 7A and 7B, the x-axis represents SOC, and the y-axis indicatesOCV or size of the charging. In FIG. 8, the x-axis indicates time, andthe y-axis denotes charging voltage of the battery cell. In FIG. 9, thex-axis shows time, and the y-axis represents a thickness of a thin filmof a solid electrolyte interface (SEI).

Referring to FIGS. 7A and 7B and FIG. 8, the battery cell (capacity of800 Wh/L for each volume) adopting cathode LCO (LiCoO₂)-anode Ni—Sn(Ni₃Sn₄) is charged according to an exemplary embodiment of the chargingmethod (mCC-CV). The OCV of the anode is estimated from a result of alow-rate charging (0.1C of a half cell) experiment using an Ni—Sn anode.Referring to

FIG. 7A, six charging sections are determined based on the changing rateof the slope of the anode OCV, and the ending point of the final sixthcharging section becomes a point of the constant voltage section. Thebattery begins being charged in the third charging section by theinitial condition (3.0 volts (V), SOC=0,085) of the battery. In anexemplary embodiment, as shown in FIG. 7B, the charging rates of 18.25C,9.87C, 3.44C and 1.4C are sequentially applied in the charging sections,and the constant voltage of 4.2 V is finally applied. The finishingcondition of the constant voltage section is less than the current of0.05C. The dphisl is predetermined to be 2×10⁻⁶V.

Referring to FIG. 8, battery charging voltages when the voltages arecharged in the same battery cell according to the CC-CV scheme arecompared. The maximum charging rate within which the lithium plating isnot generated in the LCO/Ni—Sn battery cell is 1.41C which is estimatedthrough a simulation, and the charging voltage when the LCO/Ni—Snbattery cell is charged with this charging rate is shown as a comparisonembodiment (1.41 C CC-CV).

Referring to FIG. 8, when the battery charging method according to anexemplary embodiment is applied, the charging time is reduced by equalto or greater than 58% (i.e., 47.8 minutes to 20 minutes) compared towhen a charging method according to the conventional constant currentcharging scheme is applied.

Referring to FIG. 9, the thickness of the SEI thin film (i.e., an SEIincrement) that is an index for detecting a degradation of a life-spanof the battery cell in an exemplary embodiment is 0.9 nanometer (nm), issubstantially similar to the thickness of the SEI thin film of 0.92 nmwhen the conventional CC-CV charging scheme is applied. Therefore, suchan embodiment of the battery charging method is expected to have asimilar cycle life-span characteristic to the conventional CC-CVcharging scheme. FIG. 10 shows a graph of a charging section applied toan LCO/graphite battery cell according to an exemplary embodiment, andFIG. 11 shows a graph of a comparison result of capacity retentions ofan LCO/graphite battery cell according to an exemplary embodiment.

Referring to FIG. 10, the charging section determined by the change ofthe OCV of the battery cell using the graphite that is mesoporous carbonmicro beads (“MCMB”) as the anode material is shown (S₀: 0.45). TheCC-CV charging scheme is used to find capacity retention after acharging/discharging cycle of the battery cell is repeated. A chargingstart voltage 3.0 V and SOC of 0.044 are applied as the initial state ofthe battery, the charging rates corresponding to the respective chargingsections are sequentially 2.47C, 1.9C, 1.58C, 1.24C, 1.06C and 0.94C,and the constant voltage of 4.4 V is applied to the battery in theseventh charging section. In FIG. 11, the x-axis represents thecharging/discharging cycles of the battery cell, and the y-axisindicates capacity retention of the cell measured by an experiment ofthe battery. Cases to which the charging rates of 10, 2C and 3C areapplied are used as a control group. Referring to FIG. 11, the batterycharging method according to an exemplary embodiment has shown improvedcapacity retention (equal to or greater than 90%) compared to 2C and 3Cafter fourteen cycles are performed. In the case of 10, compared to thecharging time of 120 minutes, the battery charging method according toan exemplary embodiment (OPT.1 or OPT.1′) has the charging time of 80minutes, thereby showing the 33.3% of improvement than 10 from theviewpoint of the charging time.

FIG. 12A to FIG. 12C show graphs of changes of dphisl with respect tocharging section, charging rate, and time of an LCO/graphite batterycell according to an exemplary embodiment, FIG. 13 shows a graph ofcomparison of changes of a charging voltage of an LCO/graphite batterycell according to an exemplary embodiment, and FIG. 14 shows a graph ofchanges of a thickness of an SEI thin film of an LCO/graphite batterycell according to an exemplary embodiment.

In FIG. 12A, the x-axis is SOC, and the y-axis shows the size of OCV.

In FIG. 12B and FIG. 12C, the x-axis represent time, and the y-axisindicates the charging rate and the size of dphisl. In FIG. 13, thex-axis is time, and the y-axis is the charging voltage of a batterycell. In FIG. 14, the x-axis indicates time, and the y-axis is thethickness of an SEI thin film. Referring to FIG. 12A to FIG. 12C, FIG.13, and FIG. 14, the battery cell (capacity of 800 Wh/L for each volume)adopting cathode LCO (LiCoO₂)-anode graphite is charged according to anexemplary embodiment of the charging method. Referring to FIG. 12A, sixcharging sections are determined (S₀: 0.6) based on the changing rate ofthe slope of the anode OCV, and the ending point of the final or sixthcharging section becomes a point of the constant voltage section. Thebattery begins being charged in the second charging section by theinitial condition (3.0 V, SOC=0,035) of the battery. The charging ratessequentially are 8.25C, 4.92C, 3.73C, 2.75C, 2.335C, 1.63C and 1.25C inthe respective charging sections, and the constant voltage of 4.4 Visfinally applied. The dphisl is predetermined to be 2×10⁻⁶ V.

Referring to FIG. 13, battery charging voltages when the voltages arecharged in the same battery cell according to the CC-CV scheme, and thebattery charging voltage according to a pulse charging scheme arecompared. The maximum charging rate, within which the lithium platingdoes not occur, in the LCO/graphite battery cell is 1.35C which isestimated or determined through a simulation, and the charging voltagewhen the LCO/graphite battery cell is charged with the charging rate of1.35C is shown as a comparison embodiment. The pulse charging schemerepresents the result of local optimization determined by performing thenumerical experiment more than 20 times.

Referring to FIG. 13, when the battery charging method according to anexemplary embodiment is applied, the charging time is reduced by equalto or greater than 38% (reduced form 47.7 minutes to 29.5 minutes)compared to the conventional constant current charging scheme, and thecharging time is reduced by about 14% (reduced from 34.3 minutes to 29.5minutes) compared to the pulse charging scheme.

Referring to FIG. 14, the thickness of the SEI thin film is 2.14 nm,which is similar to the thickness of 1.91 nm in a case of theconventional CC-CV charging scheme is used and the thickness of 2.03 nmin a case of the pulse charging scheme. Therefore, such an embodiment isexpected to have a similar cycle life-span characteristic to theconventional CC-CV charging scheme and the pulse charging scheme.

FIG. 15 shows a block diagram of a battery charging device according toan exemplary embodiment.

Referring to FIG. 15, an exemplary embodiment of the battery chargingdevice 1500 includes a processor 1510, a memory 1520, and a charginginterface 1530.

The memory 1520 may be connected to the processor 1510 to store variouskinds of information for driving the processor 1510 or at least oneprogram to be performed by the processor 1510. The processor 1510 mayrealize functions, processes, or methods proposed in the exemplaryembodiments of the disclosure. That is, an operation of the batterycharging device 1500 according to an exemplary embodiment of the batterycharging method may be realized by the processor 1510. The charginginterface 1530 may be connected to the battery in a wired or wirelessmanner to monitor the charging amount (a SOC or a charging voltage) ofthe battery according to control by the processor 1510 and apply thecurrent and the voltage for charging the battery to the battery.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A method for charging a battery, the methodcomprising: monitoring a state of the battery; determining, based on themonitored state of the battery, a current charging stage among aplurality of charging stages to which both a multi-stage constantcurrent charging scheme and a single stage constant voltage chargingscheme are applied; and charging the battery during the current chargingstage with a current charging rate corresponding to the current chargingstage, wherein the current charging rate corresponding to the currentcharging stage is determined so as to maintain a potential differencebetween a potential of an anode of the battery and a potential of anelectrolyte solution of the battery to be greater than zero in thecurrent charging stage.
 2. The method of claim 1, further comprising:charging the battery during a next charging stage with a next chargingrate corresponding to the next charging stage when the current chargingstage ends, wherein the next charging rate is less than the currentcharging rate.
 3. The method of claim 2, wherein the current chargingstage ends when the potential difference is determined to be equal to orless than a predetermined value.
 4. The method of claim 3, wherein thepredetermined value is 2×10⁻⁶ volt.
 5. The method of claim 1, furthercomprising: monitoring whether a charging voltage of the battery hasreached a predetermined voltage value when determined charging stage ofthe battery is a last charging stage among the plurality of chargingstages; and applying a predetermined constant charging voltage to thebattery when the charging voltage is determined to be equal to thepredetermined voltage value.
 6. The method of claim 1, wherein to theplurality of charging stages is determined based on a window with apredetermined height applied with reference to a minimum or a maximum ofa differential graph of the functional relation included in theplurality of charging stages, and the predetermined height ispredetermined according to complexity of a charging processor.
 7. Themethod of claim 6, wherein as the predetermined height increases, awidth of the window increases to increase respective lengths of theplurality of charging stages, and as the predetermined height decreases,the width of the window reduces to reduce the respective lengths of theplurality of charging stages.
 8. The method of claim 4, wherein as thepredetermined height increases, a width of the window increases toreduce a number of the plurality of charging stages, and as thepredetermined height increases, the width of the window reduces toincrease the number of the plurality of charging stages.
 9. A device forcharging a battery comprising: a processor; a memory connected to theprocessor; and a charging interface connected to the battery, whereinthe processor performs a program stored in the memory to perform:monitoring a state of the battery; determining, based on the monitoredstate of the battery, a first charging stage among a plurality ofcharging stages to which both a multi-stage constant current chargingscheme and a single stage constant voltage charging scheme are applied;and charging the battery during the first charging stage with a firstcharging rate corresponding to the first charging stage, wherein thefirst charging rate corresponding to the first charging stage isdetermined so as to maintain a potential difference between a potentialof an anode of the battery and a potential of an electrolyte solution ofthe battery to be greater than zero in the first charging stage.
 10. Thedevice of claim 9, wherein the processor performs the program stored inthe memory to further perform: charging the battery during a secondcharging stage with a second charging rate corresponding to the secondcharging stage when the first charging stage ends, wherein the secondcharging rate is less than the first charging rate.
 11. The device ofclaim 10, wherein the second charging stage starts when the potentialdifference in the first charging stage is determined to be equal to orless than a predetermined value.
 12. The device of claim 11, wherein thepredetermined value is 2×10⁻⁶ volt.
 13. The device of claim 9, whereinthe processor performs the program stored in the memory to furtherperform: monitoring whether a charging voltage of the battery hasreached a predetermined voltage value when determined charging stage ofthe battery is a last charging stage among the plurality of chargingstages; and applying a predetermined constant charging voltage to thebattery when the charging voltage is determined to be equal to thepredetermined voltage value.
 14. The device of claim 9, wherein theplurality of charging stages are determined based on a window with apredetermined height applied with reference to a minimum or a maximum ofa differential graph of the functional relation included in theplurality of charging stages, and the predetermined height ispredetermined according to complexity of a charging processor.
 15. Thedevice of claim 14, wherein as the predetermined height increases, awidth of the window increases to increase respective lengths of theplurality of charging stages, and as the predetermined height decreases,the width of the window reduces to reduce the respective lengths of theplurality of charging stages.
 16. The device of claim 14, wherein as thepredetermined height increases, a width of the window increases toreduce a number of the plurality of charging stages, and as thepredetermined height decreases, the width of the window reduces toincrease the number of the plurality of charging stages.